For a GPS receiver integrated into a cellular phone, power-consumption is an issue. Since only a limited storage of energy is available, every module inside a cellular phone should consume as little power as possible. Besides the required cellular transmitter and receiver modules, cellular phones today often include a GPS receiver module, a Bluetooth receiver module, a WLAN module, and even a camera.
There are several ways to reduce power consumption in an electrical device; e.g. the device can be miniaturized, modules/components can be selected that consume less power, or modules in the device can be selectively shut down (partially or wholly). Shutting down a module, however, is really only viable if it is possible to maintain the same level of performance with the shut down/reduced power-on time.
Of the modules now often included in cellular phones, the GPS receiver consumes significant power. There are many generally known techniques for saving power consumed by a GPS receiver (in a cellular phone or in a standalone application): Parts of the GPS receiver hardware can be shut down; for example, any excess channels not useful in tracking satellites due to poor local constellation can be powered-down. The GPS receiver hardware can be run at a lower frequency. And the GPS receiver RF (radiofrequency) front-end can be shut down and only the tracking loops at the DSP (digital signal processing) baseband run (to enable fast reacquisition). All of these methods, however, without more, can sacrifice GPS receiver performance.
For saving power in a cellular phone generally, it is noted that U.S. Pat. No. 6,067,460 for a MOBILE STATION HAVING ENHANCED STANDBY MODE discloses using motion sensors or a GPS receiver (or other devices) to determine when a user of a cellular phone might not be moving (or moving only very slowly), in which case—usually only after the user confirms both that the user is not moving and is not likely to be moving in the next several minutes—the cellular phone stops making neighbor channel measurements for DCCH (dedicated control channel) reselection, thereby saving power.
What is still needed is a way to reduce power use by a GPS receiver—in either a standalone application or in a mobile phone—without a significant sacrifice of the GPS receiver's performance.